Metallurgical lances are used for injection of a wide variety of materials into molten metals. Materials which are injected into the molten metal for metallurgical purposes may be both gaseous and particulate solids, as well as non-particulate solids, such as metallurgical wire. The purposes of such injections also vary widely, and these purposes include the injection of refining oxygen, desulfurization compounds and alloying ingredients. The tip and front portion of the lance are disposed beneath the surface of the molten metal during the injection of the materials into the melt, and the high temperatures of the molten metal cause deterioration of that tip and/or front portion. As the tip and/or front portion deteriorates, the lance becomes less effective, and in addition is subject to plugging, such that unpredictable amounts of the material are actually injected into the melt. When this occurs, the lance becomes unservicable, and the lance must be either replaced or repaired.
The more conventional lances are not repairable, and when such deterioration or plugging occur, the unservicable lance must be replaced with a new lance. Lances of the nature are relatively expensive, and the art has sought means of repairing deteriorated or plugged lances. A conventional lance has a support outer conduit, made of, for example, a thick-walled pipe, and a material carrying inner conduit, such as a smaller thick-walled pipe, which is spaced from but within the outer conduit. A high temperature insulator covers the outer conduit, at least along the portions which will be encountered by the molten metal, and more usually the insulator projects from the tip of the lance so as to provide an insulator section beyond the outer conduit. In this latter case, the inner conduit passes through that projection of the insulator and terminates at essentially the end of that projection. Such an arrangement protects the lance, and especially the inner conduit, from the deteriorating and/or plugging environment of the molten metal. It is possible for such lances to be constructed such that when the lance becomes unservicable because of deterioration or plugging of the tip or front portion of the lance, the inner conduit may be moved through the outer conduit and insulator of the lance, with the end of inner conduit passing beyond the projection of the insulator. That deteriorated or plugged portion of the inner conduit is then removed, e.g., sawed away, and the lance then becomes servicable.
However, in such constructions of such lances, there is a relatively small amount of inner conduit which can be moved through the lance and the tip and/or front portion renewed, as explained above, and after that amount of the inner conduit has been so used, the lance is no longer servicable and must be discarded. This is true even though the outer conduit and the insulator may still be quite servicable. Thus, the expensive lance must be discarded, even though most of the portions of the lance are still quite servicable.
It would, of course, be of substantial value to the art to provide a lance where this difficulty can be avoided and where the lance can remain servicable as long as the insulator and outer conduit remain servicable. The present invention provides such an improved lance and with the present improvement, the lance will remain servicable for substantial periods of time.